1. Field of the Invention
The present invention relates to a liquid-containing type vibration isolating apparatus which is used in an engine mount or the like in a vehicle such as an automobile, and which absorbs and damps vibrations from a vibration generating portion.
2. Description of the Related Art
A liquid-containing type vibration isolating apparatus has been proposed in Japanese Patent Application Laid-Open No. 60-104824 as a vibration isolating apparatus to be used in an engine mount or the like for automobiles.
In this vibration isolating apparatus, an interruption plate member separates a pressure-receiving liquid chamber and an auxiliary liquid chamber. The chambers communicate with each other via an orifice formed in the interruption plate member. Further, a plate member, which is connected to a mounting member of an engine, is disposed within the pressure-receiving liquid chamber.
In this vibration isolating apparatus, low-frequency vibrations are absorbed by liquid resonating in the orifice. High-frequency vibrations which are greater than or equal to several hundred Hz are absorbed by resonance of liquid in a vicinity of the interruption plate member.
In order to effectively absorb low-frequency vibrations, it is necessary to lengthen the path between the liquid chambers and obtain a large loss factor (tan.delta.). However, in this vibration isolating apparatus, because the liquid chambers are connected via the orifice, a large loss factor cannot be obtained.
Further, among low-frequency vibrations, there is shake vibration (e.g., vibration whose frequency is approximately 10 Hz) and idle vibration (e.g., vibration whose frequency is approximately 20 to 30 Hz), which differ from each other in frequency. Accordingly, when the orifice is tuned to the frequency of shake vibrations, the efficiency of damping idle vibrations deteriorates. Both shake vibrations and idle vibrations cannot be effectively absorbed.